One of the most important areas in cellular technology development is the exploration of ways to improve the capacity of the system. Spectral efficiency and power consumption in mobile systems are forcing wireless communications designers to explore new areas in the technology that will offer capacity relief. One of these new areas being explored is the use of directional beam antennas to improve the link margin of the forward and reverse links between a base station and a WTRU. The increased gain of the directional antenna over the typical omni-directional antenna provides increased received signal level at the WTRU receiver allowing the base station to transmit at a lower power level. This allows more users to be simultaneously active, (i.e., more capacity), and lowers the interference seen by WTRUs in adjacent cells.
Directivity of the antenna in a WTRU can also provide a reduction in the interference level from signals received from adjacent base stations. The reverse link from the WTRU to the base station enjoys the same link margin improvement, thereby allowing the WTRU to transmit at lower power level. This reduces the interference seen at base stations of adjacent cells and can lengthen the battery life at the WTRU.
The use of a directional antenna at a WTRU requires decisive reference to the signal level measurements on each of the directional beams in order to select the best directional mode of the antenna. In a mobile communication network, the WTRU must continually monitor the received signal level in each of the directional modes and periodically reselect the best directional mode to accommodate environment changes and movement of the WTRU. In a GSM network where a TDMA scheme is employed to accommodate multiple users, inactive timeslots, (i.e., where the WTRU is not required to transmit or receive), can be used to make these measurements. However, the signal level received at the WTRU constantly changes due to multi-path propagation. Thus, measuring a higher received signal level in one direction versus another at a given time may not result in the best directional beam selection.